The art of inspecting liquid filled containers, especially vials and ampoules, for the presence of particulate matter is a relatively old and crowded one as exemplified by U.S. Pat. Nos. 2,132,447 (Stout); 2,426,355 (Kellogg); 2,531,529 (Price); 3,029,349 (Schell); 3,217,877 (Honjyo et al); 3,292,785 (Calhoun); 3,415,997 (Vinzelberg et al); 3,496,369 (Makino et al); 3,528,544 (Noguchi et al); 3,598,907 (Drinkuth); 3,627,423 (Knapp et al); 3,777,169 (Walter et al); 3,830,969 (Hofstein); and 3,914,058 (Knapp et al). In each of the foregoing U.S. Patents, and also in the present case, the inspection process includes the steps of rotating a container to be inspected, suddenly stopping the rotation of the container, and then inspecting the illuminated rotating fluid for moving particles. This simplifies detection of particles since a moving illuminated particle can be easily detected and is readily distinguishable from the stationary reflection which results from container imperfections.
Many prior art systems have been developed which inspect liquid filled transparent containers with photo transducers for both large particles (e.g. glass fragments) and fine particulate matter (below 50 microns). The rotating liquid eddy or vortex produces a change in the illumination signal, which is indistinguishable from a moving particle signal. The prior art systems therefore had to wait for the vortex to disappear before the photo transducer could make an accurate reading of particulate movement. However, when small particles are present, there is a considerable possibility that they will rise to the meniscus and be flung to the wall of the container by centrifugal force, where they could cling and thereby avoid detection. The prior art systems, as for example, U.S. Pat. No. 2,531,529; were able to eliminate the effect of the vortex signal by blocking it until it was no longer appreciable. However, none of the prior art systems recognized that the interference due to the vortical meniscus decay at the liquid-container interface could be corrected thereby allowing a faster and more accurate inspection of the rotating meniscus.
Prior art systems have generally used only one or two photo transducers each of which are directed at the entire rotating solution, or as in U.S. Pat. No. 2,132,447 a plurality of photo transducers aligned in the vertical direction to allow different portions of the container to be given preferential treatment. If specular reflections from either the surface of the liquid or optical flaws in the container are of sufficient intensity, a photo transducer could saturate at its peak current. If this occurred, it would be impossible to detect any change in illumination due to particle movement at the liquid volume which was monitored by that photo transducer. Since the movement of the particles is a strongly horizontal one, if one of the vertically aligned photo transducers was so saturated, any particle in the liquid zone of that particular photo transducer would be missed.
Prior art systems have generally monitored the rotating liquid along one or two viewing axes with a single image plane being formed at each axis. If a light or heat sensitive composition was involved the intensity of the light source would have to be minimized with a resulting reduction in the range of sharp focus for the particles of interest. When the range of sharp focus of the image plane was less than the diameter of the article being inspected, it was necessary to increase the inspection time to insure that a particle of interest would be detected as it passed through the range of sharp focus.
An advantage of the invention is to provide an improved system which can inspect the entire liquid in a transparent container including the rotating meniscus for particulate contamination in a faster and more reliable manner than previous methods.
A further advantage of the invention is to provide an improved system which can inspect a liquid in a transparent container for particulate contamination with the same particle size sensitivity independent of the container size and specular reflections from the liquid surface or from marks and defects in the container.
Another advantage of the invention is to provide an improved system which can inspect light or heat sensitive compositions in a faster, more reliable manner than previous methods.